The present invention relates to clutches, particularly for automotive use, and is concerned with that type of clutch which may be controlled so that the torque which it transmits is at a predetermined level or alters in accordance with a predetermined pattern. The invention is particularly concerned with such clutches for use in connection with so-called manual automatic gearboxes.
Clutches for use with manual automotive gearboxes are inherently of torque controlled type but the torque control is effected by the user. Thus when the user releases the clutch to reconnect the engine output shaft to the gearbox after changing gear, he does so gradually so that the torque transmitted to the gearbox increases progressively to its maximum value. Gear changing is thus rendered smooth, whereas if the clutch were released suddenly gear changing would be accompanied by unacceptably jerky movement of the vehicle.
However, manual automotive gearboxes are gradually losing favour and being replaced by either automatic gearboxes or manual automatic gearboxes. Automatic gearboxes typically do not incorporate meshing pairs of gears, as are used in manual gearboxes, and their operation is generally inherently smooth. Manual automatic gearboxes, however, are generally similar to manual gearboxes and incorporate meshing pairs of gearwheels. When a gear change is to be effected, the clutch is automatically disengaged, e.g. hydraulically, and the gear selector fork moved, e.g. again hydraulically, and the clutch is then reengaged. As discussed above, in order to avoid unacceptable jerkiness, it is necessary for the clutch to be re-engaged progressively and in known torque controlled clutches this is effected by applying a progressively increasing hydraulic pressure to the hydraulic actuating piston associated with the clutch plates. However, progressive hydraulic pressure control valves are very expensive. A complex feedback system is commonly used in an attempt to achieve a predetermined profile of the rate of increase of the torque transmitted by the clutch but these systems suffer from a lack of sophistication which results in practice in the gear change being unacceptably jerky.
It is therefore the object of the invention to provide a torque-control clutch, particularly for use with a manual automatic automotive gearbox which overcomes the problems referred to above and, in particular, does not incorporate a progressive hydraulic valve and enables smooth gear changes.